New report puts real numbers behind history of oyster reefs

In an effort to advance the field of coastal restoration, The Nature Conservancy and a team of scientists from more than a dozen management agencies and research institutions led by the University of Cambridge conducted an in-depth study of oyster reef area and, for the first time, the actual biomass (the "living weight") of oyster reefs in dozens of estuaries throughout the United States.

'Historical ecology with real numbers', published today in Proceedings of the Royal Society B, presents the first truly quantitative estimates of decline in oyster habitat over such a large spatial and temporal scale.

The findings show that while that oyster reef area declined by 64% over the last century, the total biomass, or living weight of oysters on reefs, had dropped by 88% during this period, revealing that simple physical area is an unreliable indicator of habitat status.

The good news, according to lead author Dr. Philine zu Ermgassen of University of Cambridge, is that the study gives a much-needed historical picture of conditions in specific bays and estuaries, something that will aid in future restoration efforts.

"Oysters were a valuable resource, even a century ago, so government surveyors mapped vast acreages and built up a story of a critically important habitat in wonderful detail," said Dr. zu Ermgassen. "Although somewhat unfamiliar to us here in Europe the humble oyster was once so numerous, both here and in the United States, that it formed large physical structures – oyster reefs – that rose up in banks off the sea bed.

"Using meticulous records compiled 100 years ago, we have been able to accurately quantify the changes in oyster reefs over time. Anecdotes have been converted to hard facts. Of course there have been huge losses in area, but that is only part of the story. We've also noted changes in density and structure of the remaining oysters, such that what is left is a much depleted habitat. Managers and scientists need to pay closer attention to density when setting restoration or conservation objectives."

"In addition to aiding restoration, the study will inspire it," says co-author Dr. Mark Spalding, a lead scientist with The Nature Conservancy's Global Marine Program, and also based at Cambridge. Indeed, the authors are keen to point out that the US is leading the world in turning things around for these habitats, with restoration work underway in numerous estuaries to restore oyster habitat.

"This is a call to action, and these findings will provide funders and managers with a powerful baseline – a clear vision of how things were – and an opportunity to establish meaningful goals and targets. The findings have implications beyond oyster reefs, however. Almost all of our concerns about the loss of natural areas – from forests and wetlands to seagrass meadows and kelp beds – are based on an estimation of change in area," said Dr. Spalding. "This study shows that the losses may be even worse than we thought, because the quality of the remaining patches of habitat may be so diminished that it is not providing the function we expect from any given area."

Replies to This Discussion

Just one more bit of evidence that the environmental movement is on the right track. This is not a minor finding, and one that needs attention.

Would it be so heard to protect our waters, soils and air from contaminants? I don't think so. Even with this exploding population. With 7,000,000,000 human beings, we must surely wake up to that fact.

" many people believe that because as a species we've been on this planet for so long, and still have so many resources left that we've not yet consumed, that we'll be ok for a significant amount of time to come. This view however fails to take into account the exponential growth rate of the human population. Take a look at this graph of the population of the earth over time, and you'll see what I mean"

"The population of the planet is increasing at an increasing rate. On that graph, within the past 100 years, it nearly turns into a vertical line. There is no way that this kind of growth can be sustainable. To say that we may have enough resources to support the population we have now may be true ( though I've read in a variety of places that we are already past our carrying capacity of the planet), but to expect that those same resources will support the population of the future if we continue to expand at an increasing rate is at best, ludicrous."